本文档提供了一种在IP域中实现预付费电话卡应用程序的解决方案，用于电路交换的有组织呼叫。SUBSCRIBE和NOTIFY请求用于请求DTMF监控和检测通知，以便在通话过程中启用呼叫者发起的重新发起请求。

This document provides a solution for the implementation of a Pre-Paid Calling Card application in the IP domain for circuit switched orginated calls. The SUBSCRIBE and NOTIFY requests are used to request DTMF monitoring and notification of detection in order to enable caller-initiated re-origination request while a call is in progress.